This invention relates to an exhaust brake with a pressure relief device, an engine equipped with an exhaust brake and the pressure relief device, as well as to a method of preventing a buildup of excessive pressure in an exhaust brake.
Diesel engines in vehicles, particularly larger trucks, are commonly equipped with exhaust brakes for engine retarding. An exhaust brake consists of a restrictor element mounted in the exhaust system. When this restrictor closes, back pressure resists the exit of gases during the exhaust cycle and provides braking power for the vehicle.
With conventional fixed geometry exhaust brakes, the retarding power decreases sharply as engine speed decreases. This occurs because the restriction is typically optimized to generate maximum allowable back pressure at rated engine speed. The restriction is accordingly too small to be effective with the lower mass flow rates encountered at lower engine speeds.
Systems have been developed to optimize the retarding power of exhaust brakes over a range of engine speeds. One approach has been to implement pressure relief as a means to limit maximum developed exhaust pressure. Engine braking mainly occurs at lower engine speeds where exhaust pressures are lower and the pressure relief device is not active. The pressure relief device only operates when engine speeds are higher and the exhaust pressure is accordingly higher. This means that the exhaust pressure can be increased for engine braking purposes without being excessive at high engine speeds.